I see that it's possible to upgrade an AKS cluster with az aks upgrade: https://docs.microsoft.com/en-us/azure/aks/upgrade-cluster
I see that it's possible to upgrade a kubernetes cluster that has been created with acs-engine with acs-engine upgrade: https://github.com/Azure/acs-engine/tree/master/examples/k8s-upgrade
Is it possible to upgrade a kubernetes cluster that has been created with ACS?
Is it possible to upgrade a kubernetes cluster that has been created with ACS?
For now, there is no way to upgrade k8s version directly.
Since ACS is basically an IaaS offering you could perform the upgrade manually.
Here a similar case about you, please refer to it.